Heat pipe

ABSTRACT

A heat pipe includes: a container and a wick that is disposed inside the container. The container has a width, in a width direction that is orthogonal to an up-down direction and a longitudinal direction of the heat pipe, that is larger than a thickness in the up-down direction. A gap in the width direction is provided between an internal surface of the container and an external surface of the wick. A first end portion of the wick in the longitudinal direction includes concave portions depressed in the width direction at intervals in the longitudinal direction. A second end portion of the wick in the longitudinal direction does not have any concave portions. A width of the wick in the width direction is substantially equal throughout a total length of the wick in the longitudinal direction, except for a portion at which the concave portions are disposed.

CROSS REFERENCE TO RELATED APPLICATIONS

Priority is claimed to Japanese Patent Application No. 2016-227247,filed on Nov. 22, 2016, the content of which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a heat pipe.

BACKGROUND

In the past, a heat pipe which is used for heat transport from a hightemperature portion side to a low temperature portion side is known, asdisclosed in Patent Document 1. In the heat pipe, a working fluid issealed into an inside of a container, and a wick for circulating theworking fluid of a liquid phase is provided on the inside of thecontainer. An internal space of the container functions as a flow paththrough which the working fluid of a gas phase transfers to the lowtemperature portion side from the high temperature portion side, and theheat transport from the high temperature portion side to the lowtemperature portion side is made, by material transfer of the workingfluid of the gas phase. The wick has a function of recirculating theworking fluid which is condensed on the low temperature portion side tothe high temperature portion side by a capillary phenomenon, and ofmaking operation of the heat pipe maintainable.

PRIOR ART DOCUMENTS

[Patent Document 1] Japanese Unexamined Patent Application, FirstPublication No. H11-183069

Meanwhile, in such a kind of heat pipe, there is a demand to improve theefficiency of the heat transport without increasing an occupied area, inaccordance with miniaturization of a device which is mounted thereon orincrease of a heating value.

SUMMARY

One or more embodiments of the present invention improve efficiency ofheat transport, without increasing an occupied area of a heat pipe.

According to one or more embodiments of the present invention, there isprovided a heat pipe including a container into which a working fluid issealed, and a wick that is provided inside of the container, in which inthe container, the width in a width direction which is orthogonal toboth of an up-down direction and a longitudinal direction is larger thana thickness of the up-down direction, a gap in the width direction isprovided between an internal surface of the container and an externalsurface of the wick, a plurality of concave portions that becomedepressed in the width direction are formed at intervals in thelongitudinal direction, at a first end portion of the wick in thelongitudinal direction, the concave portion is not formed at a secondend portion of the wick in the longitudinal direction, and a width ofthe wick in the width direction is substantially equal throughout atotal length of the wick in the longitudinal direction, except for aportion at which the concave portion is formed.

According to one or more embodiments, since the plurality of concaveportions that become depressed in the width direction are formed at theintervals in the longitudinal direction, at the first end portion of thewick, it is possible to make a surface area of the wick large, withoutincreasing an occupied area of the whole heat pipe.

Thereby, the working fluid with which the wick is impregnated is capableof being efficiently evaporated from the concave portion having thelarge surface area, and transfer of the working fluid of a gas phase toa low temperature portion side from a high temperature portion side ispromoted, thereby, it is possible to improve the efficiency of heattransport.

Furthermore, the concave portion is not formed other than the first endportion, and the width of the wick in the longitudinal direction issubstantially equal throughout the total length, except for the portionat which the concave portion is formed. In this manner, there is noportion of which the width of the wick is narrow other than anevaporation portion, thereby, flow resistance of the working fluid of aliquid phase does not become large. Accordingly, it is possible toefficiently transfer the working fluid of the liquid phase.

Regarding a heat pipe according to one or more embodiments of thepresent invention, a liquid reservoir of the working fluid, which isextended in the longitudinal direction, is formed inside of the wick,and the liquid reservoir is disposed at different position from theconcave portion in the longitudinal direction, within the wick.

According to one or more embodiments, since the liquid reservoir of theworking fluid, which is extended in the longitudinal direction, isformed inside of the wick, when the working fluid evaporates from theexternal surface of the wick, it is possible to supply the working fluidof the liquid phase from the liquid reservoir toward the externalsurface. Thereby, a supply quantity of the working fluid of the liquidphase to the external surface of the wick is stabilized, and theexternal surface of the wick is capable of being preventing from drying.Therefore, it is possible to prevent an evaporation quantity of theworking fluid from being lowered by drying of the external surface ofthe wick, and to prevent the efficiency of the heat transport from beinglowered.

Furthermore, since the liquid reservoir is disposed at the positionwhich is different from the concave portion in the longitudinaldirection, it is prevented that heat is transmitted directly to theworking fluid in the liquid reservoir from a heat source. Thereby, forexample, it is possible to prevent the working fluid from suddenlyevaporating in the liquid reservoir, and it is possible to prevent theevaporated working fluid from flowing backward, toward the lowtemperature portion side in the liquid reservoir.

According to one or more embodiments of the present invention, there isprovided a heat pipe including a container into which a working fluid issealed, and a wick that is provided inside of the container, in which agap is provided between an internal surface of the container and anexternal surface of the wick, an uneven portion is formed at least onthe external surface at a first end portion of a longitudinal direction,within the wick, a liquid reservoir of the working fluid, which isextended in the longitudinal direction, is formed inside of the wick,and the liquid reservoir is disposed at different position from theuneven portion in the longitudinal direction.

According to one or more embodiments, in a case where the heat pipe isdisposed with respect to the heat source such that the heat source ispositioned in the vicinity of the uneven portion, the working fluidwhich receives the heat from the heat source efficiently evaporates fromthe external surface of the uneven portion. Furthermore, since theliquid reservoir is disposed at the position which is different from theuneven portion in the longitudinal direction, it is prevented that theheat is transmitted directly to the working fluid in the liquidreservoir from the heat source. Thereby, for example, it is possible toprevent the working fluid from suddenly evaporating in the liquidreservoir, and it is possible to prevent the evaporated working fluidfrom flowing backward, toward the low temperature portion side in theliquid reservoir.

Regarding a heat pipe according to one or more embodiments of thepresent invention, the wick is formed of a mesh material.

According to one or more embodiments, for example, the wick is capableof being formed from a plate-shaped mesh material with die cutting, andit is possible to easily form the wick, even if a shape of the unevenportion is complicated.

Regarding a heat pipe according to one or more embodiments of thepresent invention, the wick is joined to an upper wall and a lower wallof the container.

According to one or more embodiments, the wick is securely fixed in thecontainer. Thereby, for example, even in a case where the heat pipe isbent, the wick transfers in the width direction within the container,and it is possible to prevent the gap from becoming narrow.

Regarding a heat pipe according to one or more embodiments of thepresent invention, the liquid reservoir of the working fluid, which isextended in the longitudinal direction, is formed inside of the wick,and a width of the liquid reservoir in a width direction which isorthogonal to both of the longitudinal direction and an up-downdirection is smaller than a width of a portion of the wick which isadjacent to the liquid reservoir.

According to one or more embodiments, the width of the liquid reservoiris narrow to a certain extent, thereby, it is possible to causecapillary force to act on the working fluid of the liquid phase in theliquid reservoir. Therefore, due to the capillary force, it is possibleto more smoothly recirculate the working fluid of the liquid phase inthe liquid reservoir to the high temperature portion side from the lowtemperature portion side.

According to one or more embodiments of the present invention, it ispossible to improve efficiency of heat transport, without increasing anoccupied area of a heat pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a heat pipe according to one or moreembodiments in a plane which is orthogonal to an up-down direction.

FIG. 2A is a sectional view of the heat pipe taken along A-A arrow inFIG. 1.

FIG. 2B is a sectional view of the heat pipe taken along B-B arrow inFIG. 1.

FIG. 3 is a sectional view of an uneven portion according toModification Examples in a plane which is orthogonal to a longitudinaldirection.

DETAILED DESCRIPTION

Hereinafter, a configuration of a heat pipe according to one or moreembodiments will be described with reference to FIG. 1 to FIG. 3. Ineach drawing which is used in the following description, in order tomake a shape of each member have a recognizable size, the scale thereofis appropriately changed.

As shown in FIG. 1, a heat pipe 1 includes a container 2 into which aworking fluid is sealed, and a wick 3 that is provided on an inside ofthe container 2.

Direction Definition

Here, in the present embodiments, a positional relationship of eachconfiguration will be described by setting an XYZ orthogonal coordinatesystem. An X direction is a longitudinal direction in which the heatpipe 1 and the container 2 extend. The heat pipe 1 is formed into a flatshape of which a thickness is small in a Z direction, and a width islarge in a Y direction, in a cross sectional view which is orthogonal tothe longitudinal direction. Hereinafter, the X direction is referred toas a longitudinal direction, the Y direction is referred to as a widthdirection, and the Z direction is referred to as an up-down direction.

The inside of the container 2 is hollow, and is hermetically sealed. Itis possible to appropriately select a material of the container 2, byconditions such as a kind of the working fluid and a workingtemperature. In particular, in a case where a metal material such ascopper or aluminum of which heat conductivity is high is used, it ispossible to enhance heat transportability or heat diffusibility. It ispossible to form the container 2, for example, using a metal tube suchas a copper tube, an aluminum tube, or a stainless tube.

The container 2 is formed into the flat shape of which the width in thewidth direction which is orthogonal to both of the up-down direction andthe longitudinal direction is larger than the thickness of the up-downdirection. As an example of the size of the container 2, the width ofthe width direction is approximately 7 mm, a length of the longitudinaldirection is approximately 100 mm, a height of the up-down direction ofan internal space is approximately 0.27 mm, and a wall thickness isapproximately 0.08 mm.

On the inside of the wick 3, a large number of fine pores which causecapillary force to be generated are formed. As a material of the wick 3,for example, it is possible to use a sintered body (porous sinteredbody) of a metal extra fine wire fiber, a metal mesh, and metal powder.In a case where the wick 3 is formed of a mesh material such as metal,it is possible to easily form the wick 3, even if the wick 3 has acomplicated shape, for example, from a plate-shaped mesh material withdie cutting. In a case where the wick 3 is formed of the sintered bodyof the metal powder, the size of the fine pore is capable of being madefurther smaller, and it is possible to enhance the heat transportabilityby causing the high capillary force to be generated.

The fine pore in the wick 3 is impregnated with the working fluid. Theworking fluid is a fluid which is capable of being evaporated byheating, and being condensed by heat radiation. It is possible toappropriately select the kind of the working fluid in accordance withthe temperature at which the heat pipe 1 is used, or the like. As aworking fluid, for example, it is possible to use water, alcohol,alternative freon, or the like. The working fluid may be sealed into theinside of the container 2, for example, in a state in whichnon-condensable gas such as air is degassed from the inside of thecontainer 2 in a vacuum chamber.

As shown in FIG. 1, the wick 3 is disposed along the longitudinaldirection in the container 2.

In the width direction, the width of the wick 3 is smaller than thewidth of the container 2, and the wick 3 is disposed at a center portionof the width direction of the container 2. Therefore, a gap S is formedin the width direction, between an external surface of the wick 3 and aninternal surface of the container 2. The gaps S are provided on bothsides in the width direction of the wick 3, and are extended in thelongitudinal direction. The gap S becomes a circulation path for theworking fluid of a gas phase. The width of the gap S in the widthdirection is, for example, approximately 1.7 mm.

The wick 3 is partially melted by being sintered in the container 2, andis fixed to the internal surface of the container 2. In more detail, asshown in FIG. 2A and FIG. 2B, the wick 3 is joined to an upper wall 2 aand a lower wall 2 b of the container 2. For example, in a state inwhich the wick 3 is disposed in the container 2, the container 2 isdeformed by being compressed in the up-down direction, and the wick 3 isinterposed between the upper wall 2 a and the lower wall 2 b of thecontainer 2, thereby, the wick 3 may be fixed.

Here, in the present embodiments, as shown in FIG. 1, a plurality ofconcave portions 3 a 1 which become depressed in the width direction areformed at intervals in the longitudinal direction, on the externalsurface of the wick 3. Thereby, an uneven portion 3 a is formed on theexternal surface of the wick 3, the external surface forming the gap S.Hereinafter, a portion except for the concave portion 3 a 1 is referredto as a projection portion 3 a 2, within the uneven portion 3 a. Theuneven portion 3 a is formed on the external surface at a first endportion 31 (end portion of a −X side, in the example shown in thedrawing) in the longitudinal direction, within the wick 3. The unevenportions 3 a may be formed at both end portions of the wick 3 in thelongitudinal direction. On the inside of the wick 3, a liquid reservoir3 b of the working fluid is formed.

Due to the uneven portion 3 a, it is possible to increase a surface areaof the wick 3, without increasing an occupied area of the wick 3.

The size (dimensions in the longitudinal direction and the widthdirection) of the concave portion 3 a 1 which forms the uneven portion 3a is larger than an average diameter of the fine pores in the wick 3. Ona surface of the uneven portion 3 a, a large number of fine pores of thewick 3 are open. It is possible to form the uneven portion 3 a, forexample, when the wick 3 is formed by taking out the plate-shaped meshmaterial with the mold. The uneven portion 3 a may be formed to have asize such that an uneven shape thereof is visible.

The liquid reservoir 3 b is filled with the working fluid of a liquidphase. The liquid reservoir 3 b is disposed at a middle portion 33between the first end portion 31 and a second end portion 32 of the wick3, in the longitudinal direction, and is extended along the longitudinaldirection, on the inside of the wick 3. The liquid reservoir 3 b isformed at a position which is different from the uneven portion 3 a inthe longitudinal direction, within the wick 3. As shown in FIG. 1 andFIG. 2A, the liquid reservoir 3 b passes through the middle portion 33of the wick 3 in the up-down direction. The width of the liquidreservoir 3 b in the width direction is set such that the capillaryforce is generated, and is, for example, approximately 0.6 mm. The widthof the liquid reservoir 3 b is larger than the average diameter of thefine pores in the wick 3. In the width direction, the width of theliquid reservoir 3 b is smaller than the width of a portion of the wick3 which is adjacent to the liquid reservoir 3 b in the width direction.

Here, as shown in FIG. 1, the width of the width direction of a portionat which the concave portion 3 a 1 is not formed within the first endportion 31, that is, the projection portion 3 a 2 is referred to as W1.The width of the width direction of the second end portion 32 isreferred to as W2, and the width of the width direction of the middleportion 33 is referred to as W3. At this time, the respective dimensionsof W1, W2, and W3 are substantially equal to each other. In other words,the width of the wick 3 in the width direction is substantially equalthroughout the total length of the wick 3 in the longitudinal direction,except for a portion at which the concave portion 3 a 1 is formed.

In a cross section which is orthogonal to the longitudinal direction, asectional area of the second end portion 32 becomes substantially equalin the longitudinal direction, since W2 is fixed. In the cross sectionwhich is orthogonal to the longitudinal direction, the sectional area ofthe middle portion 33 becomes substantially equal in the longitudinaldirection, since W3, and the width of the liquid reservoir 3 b which isdisposed on the inside of the middle portion 33 are fixed. In thismanner, the sectional area of the second end portion 32 or the middleportion 33 is not changed in the longitudinal direction, thereby, it ispossible to suppress flow resistance of the working fluid of the liquidphase so as to be small.

Next, operation of the heat pipe 1 which is configured as describedabove will be described.

The heat pipe 1 is attached to an electronic component or the like in acommodity (for example, a notebook PC or a mobile phone) which becomes atarget of heat transport. In the example of FIG. 1, the heat pipe 1 isdisposed over a high temperature portion H and a low temperature portionL which are represented by two-dot chain lines. The high temperatureportion H is, for example, a heat generation portion such as a CPU, andthe low temperature portion L is, for example, a heat radiation portionsuch as a heat sink.

In the vicinity of the high temperature portion H, the working fluid inthe wick 3 evaporates by being heated through a wall surface of thecontainer 2. Here, the first end portion 31 of the wick 3 is disposed inthe vicinity of the high temperature portion H, and the uneven portion 3a is formed at the first end portion 31. Therefore, the surface area ofthe wick 3 is large in the first end portion 31, and it is possible toefficiently evaporate the working fluid. The working fluid evaporates,thereby, a pressure of a gas in the vicinity of the high temperatureportion H is raised. Thereby, shown by an arrow F1 in FIG. 1, theworking fluid which becomes the gas phase transfers in the gap S towardthe low temperature portion L side in the longitudinal direction.

The working fluid of the gas phase which reaches the vicinity of the lowtemperature portion L is condensed by a loss of the heat through thewall surface of the container 2, and becomes a droplet to be bonded tothe wall surface of the container 2. The droplet of the working fluidsoaks the fine pore in the second end portion 32 of the wick 3 due tothe capillary force, as shown by an arrow F2 in FIG. 1. Here, a portionof the working fluid of the liquid phase which soaks the fine pore inthe wick 3 flows into the liquid reservoir 3 b, as shown by an arrowF2′.

The working fluid of the liquid phase in the fine pore of the second endportion 32 of the wick 3, and the working fluid of the liquid phase inthe liquid reservoir 3 b transfer to the high temperature portion H sideof the longitudinal direction due to the capillary force. Here, sincethe uneven portion is not formed in the second end portion 32 and themiddle portion 33, it is possible to efficiently transfer the workingfluid. This is because the resistance of the working fluid becomeslarge, in a case where there is a spot at which the width of the wick 3is partially narrow. Therefore, the working fluid of the liquid phase issupplied by two paths shown by arrows F3 and F4, from the fine pore inthe wick 3 and the liquid reservoir 3 b to the uneven portion 3 a. Theworking fluid of the liquid phase which reaches the uneven portion 3 aevaporates again from the surface of the uneven portion 3 a.

The working fluid which evaporates to become the gas phase transfers tothe low temperature portion L side through the gap S again. In thismanner, in the heat pipe 1, phase transition between the liquid phaseand the gas phase of the working fluid is repeatedly used, thereby, itis possible to repeatedly transport the heat which is recovered on thehigh temperature portion H side of the longitudinal direction to the lowtemperature portion L side.

As described above, according to the heat pipe 1 of the presentembodiments, since the uneven portion 3 a is formed in the wick 3, it ispossible to make the surface area of the wick 3 large, withoutincreasing the occupied area of the whole heat pipe 1. Thereby, theworking fluid with which the wick is impregnated is capable of beingefficiently evaporated from the uneven portion 3 a having the largesurface area, and the transfer of the working fluid of the gas phase tothe low temperature portion L side from the high temperature portion Hside is promoted, thereby, it is possible to improve efficiency of theheat transport.

Furthermore, the uneven portion 3 a is not formed in the second endportion 32 and the middle portion 33, and the widths W2 and W3 aresubstantially equal to each other, thereby, there is no portion of whichthe width of the wick 3 is narrow other than an evaporation portion.Accordingly, it is possible to efficiently transfer the working fluid,without making the flow resistance of the working fluid of the liquidphase large.

Since the liquid reservoir 3 b of the working fluid is formed in themiddle portion 33 of the wick 3, when the working fluid evaporates fromthe external surface of the wick 3, it is possible to supply the workingfluid of the liquid phase from the liquid reservoir 3 b toward theexternal surface. Thereby, a supply quantity of the working fluid of theliquid phase to the external surface of the wick 3 is stabilized, andthe external surface of the wick 3 is capable of being preventing fromdrying. Therefore, it is possible to prevent an evaporation quantity ofthe working fluid from being lowered by drying of the external surfaceof the wick 3, and to prevent the efficiency of the heat transport frombeing lowered.

In a case where the heat pipe 1 is disposed with respect to a heatsource such that the high temperature portion H is positioned in thevicinity of the uneven portion 3 a, the working fluid which receives theheat from the high temperature portion H efficiently evaporates from theexternal surface of the uneven portion 3 a. Furthermore, since theliquid reservoir 3 b is disposed at the position which is different fromthe uneven portion 3 a in the longitudinal direction, it is preventedthat the heat is transmitted directly to the working fluid in the liquidreservoir 3 b from the heat source. Thereby, for example, it is possibleto prevent the working fluid from suddenly evaporating in the liquidreservoir 3 b, and it is possible to prevent the evaporated workingfluid from flowing backward, toward the low temperature portion L sidein the liquid reservoir 3 b.

In a case where the mesh material is adopted as a material of the wick3, it is possible to form the wick 3, for example, from the plate-shapedmesh material with die cutting. Thereby, even in a case where the shapeof the uneven portion 3 a is complicated, it is possible to easily formthe wick 3.

In the width direction, the width of the liquid reservoir 3 b isnarrower than the width of the portion of the wick 3 which is adjacentto the liquid reservoir 3 b in the width direction, thereby, it ispossible to cause the capillary force to act on the working fluid of theliquid phase in the liquid reservoir 3 b. Therefore, due to thecapillary force, it is possible to more smoothly recirculate the workingfluid of the liquid phase in the liquid reservoir 3 b to the hightemperature portion H side from the low temperature portion L side.

The technical scope of the present invention is not limited to theembodiments described above, and it is possible to add variousmodifications thereto, within the scope without departing from the gistof the present invention.

For example, in the embodiments described above, the heat pipe 1 isextended into a straight line shape in the longitudinal direction, butthe heat pipe 1 is not limited thereto, and the heat pipe 1 may be usedin a bended manner. At that time, since the wick 3 is joined to theupper wall 2 a and the lower wall 2 b of the container 2, even if theheat pipe 1 is bent, the wick 3 transfers in the width direction withrespect to the container 2, and it is prevented that the gap S becomesnarrow. In a case where the heat pipe 1 is bent, the longitudinaldirection is a direction in which a center line of the heat pipe 1 isextended, and it is possible to define the width direction as adirection which is orthogonal to both of the center line and the up-downdirection.

In the example shown in FIG. 1, in a planar view which is seen from theup-down direction, a position of a center of the portion at which theuneven portion 3 a is formed within the wick 3 matches up with aposition of a center of the high temperature portion H, but the presentinvention is not limited thereto, and the high temperature portion H maybe positioned at a position shifted from the uneven portion 3 a.

In the embodiments described above, the uneven portion 3 a and theliquid reservoir 3 b are formed at positions which are different fromeach other in the longitudinal direction, but the present invention isnot limited thereto. For example, the liquid reservoir 3 b and theuneven portion 3 a may be formed at positions which are the same in thelongitudinal direction. Alternatively, a configuration in which such aliquid reservoir 3 b is not formed may be adopted.

In the embodiments described above, the uneven portion 3 a is formedonly in a portion of the external surface of the wick 3, but the presentinvention is not limited thereto. For example, the uneven portion 3 amay be formed on the whole of the external surface of the wick 3.

The uneven portion 3 a of the embodiments described above is formed bythe concave portion 3 a 1 which becomes depressed in the width directionof the wick 3, but the present invention it is not limited thereto. Forexample, the uneven portion 3 a may be formed by the projection portion3 a 2 which protrudes in the width direction of the wick 3.

Moreover, the uneven portion 3 a of the embodiments described above isformed by disposing the plurality of concave portions 3 a 1 on theexternal surface of the wick 3, and the sizes of the respective concaveportions 3 a 1 or the intervals between the concave portions 3 a 1 inthe longitudinal direction are substantially equal to each other, butthe present invention is not limited thereto. For example, an unevenshape in which the concave portions 3 a 1 are non-uniformly formed maybe adopted such that the surface area of the wick 3 is the largest, in aportion of which the temperature is the highest within the hightemperature portion H.

In the example shown in FIG. 2B, the width of the uneven portion 3 a,and the invention is not limited thereto. For example, as shown in FIG.3, the surface area of the wick 3 may be increased, by forming theuneven portion 3 a and the concave portion 3 a 1 such that the widthsare non-uniform in the up-down direction. It is possible to easily formthe shape of the wick 3 shown in FIG. 3, for example, by stacking aplurality of sheet-shaped wicks of which the widths are different fromeach other in the up-down direction.

In addition, within the scope without departing from the gist of thepresent invention, it is possible to appropriately replace aconfiguration element in the embodiments described above with a knownconfiguration element, and the embodiments described above may beappropriately combined with Modification Examples.

REFERENCE SIGNS LIST

-   -   1: heat pipe    -   2: container    -   2 a: upper wall    -   2 b: lower wall    -   3: wick    -   3 a: uneven portion    -   3 a 1: concave portion    -   3 a 2: projection portion    -   3 b: liquid reservoir    -   31: first end portion    -   32: second end portion    -   33: middle portion    -   S: gap

1. A heat pipe comprising: a container into which a working fluid is sealed; and a wick that is disposed inside of the container, wherein the container has a width, in a width direction that is orthogonal to both an up-down direction and a longitudinal direction of the heat pipe, that is larger than a thickness in the up-down direction, a gap in the width direction is provided between an internal surface of the container and an external surface of the wick, a first end portion of the wick in the longitudinal direction comprises a plurality of concave portions depressed in the width direction at intervals in the longitudinal direction, a second end portion of the wick in the longitudinal direction does not have any concave portions, and a width of the wick in the width direction is substantially equal throughout a total length of the wick in the longitudinal direction, except for a portion at which the plurality of concave portions is disposed.
 2. The heat pipe according to claim 1, wherein the wick further comprises a liquid reservoir of the working fluid that extends in the longitudinal direction and is disposed at a different position from any one of the plurality of concave portions in the longitudinal direction within the wick.
 3. A heat pipe comprising: a container into which a working fluid is sealed; and a wick that is disposed inside of the container, wherein a gap is provided between an internal surface of the container and an external surface of the wick, at least the external surface at a first end portion of a longitudinal direction, within the wick, has an uneven portion, a liquid reservoir of the working fluid that extends in the longitudinal direction is disposed inside of the wick at a different position from the uneven portion in the longitudinal direction.
 4. The heat pipe according to claim 1, wherein the wick is made of a mesh material.
 5. The heat pipe according to claim 1, wherein the wick is joined to an upper wall and a lower wall of the container.
 6. The heat pipe according to claim 2, wherein the liquid reservoir of the working fluid extending in the longitudinal direction is disposed inside of the wick, and a width of the liquid reservoir in the width direction is smaller than a width of a portion of the wick that is adjacent to the liquid reservoir.
 7. The heat pipe according to claim 3, wherein the wick is made of a mesh material.
 8. The heat pipe according to claim 3, wherein the wick is joined to an upper wall and a lower wall of the container.
 9. The heat pipe according to claim 3, wherein a width of the liquid reservoir in a width direction orthogonal to both the longitudinal direction and an up-down direction is smaller than a width of a portion of the wick that is adjacent to the liquid reservoir. 